CSC309 Final Lecture

Transcription

1 CSC309 Final Lecture

2 Final Exam No aids allowed Some programming - vanilla JavaScript Short answer type questions Some code reading Comprehensive (except Chrome extensions)

3 PLEASE HAND IN UNIVERSITY OF TORONTO Faculty of Arts and Science St. George Campus DECEMBER 2016 EXAMINATIONS CSC 309H1F Instructor: Karen Reid Duration: 3 hours PLEASE HAND IN Examination Aids: None Student Number: Last (Family) Name(s): First (Given) Name(s): Do not turn this page until you have received the signal to start. (In the meantime, please fill out the identification section above, and read the instructions below carefully.) Marking Guide # 1: /10 This final examination consists of 8 questions on 15 pages. A mark of at least 29 out of 73 on this exam is required to pass this course. When you receive the signal to start, please make sure that your copy of the examination is complete. Answers that contain a mixture of correct and incorrect or irrelevant statements will not receive full marks. # 2: /8 # 3: /10 # 4: /6 # 5: /7 # 6: /8 # 7: /10 # 8: /14 Good Luck! TOTAL: /73

4 DECEMBER 2016 Final Examination CSC 309H1F Note: You may detach this page for easier reference. Basic JavaScript JSON.parse() JSON.stringify() document.getelementbyid(string) document.getelementsbytagname(string) document.createelement(string) element.innerhtml element.apend(element) element.empty() alert(value) array.length() array.push() array.splice() object.tojson() event.preventdefault() JQuery $(selector).append() $(selector).html() $(selector).empty() $(selector).parent() $(selector).insertafter() $(selector).on() Express route handling req.send() req.get() req.params() req.query() req.body() req.route()

5 Topics Browser HTML5 CSS DOM Forms Validation JQuery React Server Node Express MongoDB/Mongoose Validation JSON REST Templates

6 Topics Communication HTTP GET, POST, PUT, DELETE Sessions, Cookies Security Promises (basic idea) Web Sockets (basic idea) AJAX JSON

7 Not on Final Exam Kate Hudson s talk on Data-driven decision making Chrome extensions Today s material

8 What haven t we talked about? Testing! Large Scale Web Apps Search Engines Microservices

9 Testing Functionality Tests - Unit tests: E.g. Mocha - Integration tests - End-to-end - E.g. Selenium - HTML CSS validation - forms and form validation - cookies - test for correct operation and deletion

10 Testing Usability testing - need real people to test your application - navigation - consistency - content

11 Testing Interface testing - application - requests sent to server and results displayed - web server - handles all requests correctly - database server - queried give expected results - when connection between layers fails, appropriate error messages Database testing - integrity - response time - data retrieved is shown accurately

12 Testing Compatibility testing - works on all major browsers, including older versions Performance testing - load test - normal and peak - stress test - push beyond peak - crash recovery Security testing - regularly audit!

13 Standard Web App HTTP LAN

14 Large Scale Web App HTTP LAN

15 Scale-out Expand capacity by adding more instances Pros: - can scale to fill needs by adding and removing instances - fault tolerance Cons: - manage multiple instances and distribute work

16 Scale Out: Which server to send to? Browsers want to speak HTTP to a web server - Use load balancing to distribute incoming HTTP requests across many front- end web servers HTTP redirection: - Front-end machine accepts initial connections - Redirects them among an array of back-end machines DNS (Domain Name System) load balancing: - Specify multiple targets for a given name - Handles geographically distributed system - DNS servers rotate among those targets - How to handle sessions?

17 Load-balancing switch ("Layer 4-7 Switch") Special load balancer network switch - Incoming packets pass through load balancer switch between Internet and web servers - Load balancer directs TCP connection request to one of the many web servers - Load balancer will send all packets for that connection to the same server. In some cases the switches are smart enough to inspect session cookies, so that the same session always goes to the same server. Stateless servers make load balancing easier (different requests from the same user can be handled by different servers). Can select web server based on random or on load estimates

18 nginx Web server designed for scalability Load balancer - can handle SSL processing - application health checks (server fails) - session persistence - limits to mitigate DOS - bandwidth limiting

19 Scale-out assumptions Any server will do - Different requests from the same user can be handled by different servers - Requires database be shared across servers What about session state? - should be fast because it is accessed on every request Web sockets? - cannot load balance each request

20 Scale-out storage Data sharding - spread database across instances - each piece of the database is called a shard - Tolerate failures (and improve performance) by replication - Increases complexity - Applications must place data across multiple databases

21 Memcache Main memory caching system Key-value store (both keys and values are arbitrary blobs) Used to cache results of recent database queries Much faster than databases: microsecond access time, vs. 10's of milliseconds - Writes still go to database, so no performance improvement - Cache misses still hurt performance - Must manage consistency in software (flush memcache data when database is modified)

22 Scalability Building this architecture is hard! Need data centre expertise Figuring out the right number of components is hard Cloud computing: - allows for dynamic addition and removal of resources - outsources data centre management

23 The End All the best on remaining assignments and exams. Happy Holidays!